Sequential developmental acquisition of cotransmitters in identified sensory neurons of the stomatogastric nervous system of the lobsters,Homarus americanus andHomarus gammarus

Abstract

We studied the developmental acquisition of three of the cotransmitters found in the gastropyloric receptor (GPR) neurons of the stomatogastric nervous systems of the lobsters Homarus americanus and Homarus gammarus. By using wholemount immunocytochemistry and confocal microscopy, we examined the distribution of serotonin‐like, allatostatin‐like, and FLRFNH2‐like immunoreactivities within the stomatogastric nervous system of embryonic, larval, juvenile, and adult animals. The GPR neurons are peripheral sensory neurons that send proprioceptive information to the stomatogastric and commissural ganglia. In H. americanus, GPR neurons of the adult contain serotonin‐like, allatostatin‐like, and Phe‐Leu‐Arg‐Phe‐amide (FLRFNH2)‐like immunoreactivities. In the stomatogastric ganglion (STG) of the adult H. americanus and H. gammarus, all of the serotonin‐like and allatostatin‐like immunoreactivity colocalizes in neuropil processes that are derived exclusively from ramifications of the GPR neurons. In both species, FLRFNH2‐like immunoreactivity was detected in the STG neuropil by 50% of embryonic development (E50). Allatostatin‐like immunoreactivity was visible first in the STG at approximately E70–E80. In contrast, serotonin staining was not clearly visible until larval stage I (LI) in H. gammarus and until LII or LIII in H. americanus. These data indicate that there is a sequential acquisition of the cotransmitters of the GPR neurons. J. Comp. Neurol. 408:318–334, 1999. © 1999 Wiley‐Liss, Inc.

Octopamine Modulates the Axons of Modulatory Projection Neurons

“…These data are consistent with a number of previous studies in both C. borealis and other species that reported immunostained punctate structures for amines and peptides in the stn-son junction (Marder et al, , 1987Callaway et al, 1987;Mortin and Marder, 1991;Kilman et al, 1999;Skiebe, 1999;Skiebe et al, 1999). These punctate structures are found within the nerve where most of the modulatory axons coming from the CoGs and the OG are located.…”

“…2 A) (Marder et al, , 1987Kilman et al, 1999;Skiebe, 1999;Skiebe et al, 1999), suggesting that this region is a potential site for synaptic and/or modulatory interactions among fibers traveling in the stn. We labeled the fibers projecting from the ion to the stn by backfilling the ion fibers with neurobiotin and then immunostaining these preparations for synaptotagmin (Fig.…”

“…Therefore, this site is special, because it is the first anatomical location at which bilaterally arising neuronal pathways can interact. Interestingly, numerous immunocytochemical studies have shown areas of what appear to be neuropilar-like varicosities and branches in this location (Marder et al, , 1987Kilman et al, 1999;Skiebe, 1999;Skiebe et al, 1999), and this is also a site at which synapses are seen (Kilman, 1998;Skiebe and Ganeshina, 2000;Skiebe and Wollenschlager, 2002). We now find that the axons of the MCN5 neurons are sensitive to octopamine at this site and that the ef-fects of octopamine on the pyloric rhythm of the crab depend both on its actions on the STG itself and on the axons of the MCN5 neurons.…”

Ontogeny of Modulatory Inputs to Motor Networks: Early Established Projection and Progressive Neurotransmitter Acquisition

“…Neuromodulatory systems involved in the control of central pattern generators (CPGs) have been extensively studied in terms of neuronal population, neurotransmitter phenotype, and alteration of network activity. A large body of work has been devoted to the progressive developmental acquisition of projection neurons using retrograde dye migration (Cabana and Martin, 1984;van Mier and ten Donkelaar, 1984;Okado and Oppenheim, 1985;Kudo et al, 1993) and of neuromodulatory substances using immunocytochemistry (Senba et al, 1982;Commissiong, 1983;Sako et al, 1986;van Mier et al, 1986;Rajaofetra et al, 1989;Pindzola et al, 1990;Fenelon et al, 1998aFenelon et al, , 1999Kilman et al, 1999). Using these approaches, it has been concluded that progressive acquisition of neuromodulatory substances by a target network is associated with axonal ingrowth of descending neurons (Sako et al, 1986;van Mier et al, 1986;Pindzola et al, 1990).…”

“…Using these approaches, it has been concluded that progressive acquisition of neuromodulatory substances by a target network is associated with axonal ingrowth of descending neurons (Sako et al, 1986;van Mier et al, 1986;Pindzola et al, 1990). However, some studies seem to indicate that projection neurons may reach their targets before expressing their adult neurotransmitter complement (Henderson, 1991;Kilman et al, 1999). To investigate whether such ontogenetic processes may exist in descending systems, we combined retrograde dye migration to label embryonic neurons reaching their target networks, and immunocytochemical detection of neuromodulatory substances.…”